Studies On The Kinetics Of Sodium Gluconate Fermentation And Crystallization Process

Sodium gluconate is a polyhydroxy organic salt, which possesses many excellent characteristics. It has a broad purpose in the food, medicine, chemical and construction industries. The crystallization properties and crystallization processes of sodium gluconate, the kinetic models for sodium gluconate batch fermentation by Aspergillus niger were mainly studied in this paper.First, based on the previous research in our lab, the kinetics for sodium gluconate batch fermentation by Aspergillus niger preserved in our lab were studied. Through the optimal parameters estimation and nonlinear fitting method, kinetic models were proposed by using the Logistic equation for cell growth, the Luedeking-Piret equation for sodium gluconate production and the Luedeking-piret/like equation for glucose consumption. The calculated results of models were compared with experimental data, the results showed the experiment and model values were in a good agreement, the average relative error of three models is 3.36%, 4.95% and 3.21%, respectively. The models provided a reasonable description for the batch fermentation process, which provided theoretical basis for studying the enlargement experiment, fed-batch fermentation and even continuous fermentation.Then, the crystallization thermodynamics of sodium gluconate were explored. The influences of temperature, solvent composition, pH and impurities on its solubility were studied. The results showed that sodium gluconate had very high solubility in aqueous solution, it reached 61.53g at 25℃; sodium gluconate was slightly soluble in ethanol, the solubility of sodium gluconate decreased with adding ethanol; the solubility of sodium gluconate was independent of pH between pH 4 and 7; the residual glucose in the fermentation borth had little effects on solubility of sodium gluconate, but the solubility of sodium gluconate decreased with adding sodium citrate. The width of crystallization metastable zone was also obtained, and all of these provided a thermodynamic basis for studying on the crystallization of sodium gluconate.On the basis of research on crystallization thermodynamics of sodium gluconate, the vacuum evaporative crystallization technology of sodium gluconate in fermentation broth was studied. The crystallization technology was optimized by evaluation of medium size and coefficient of variation of the crystals. By examining several major factors including seed load, evaporation temperature, feed concentration, stirring rate, vacuum degree and so on, the single factor test and the orthogonal test were conducted. In the orthogonal test, we obtained the optimum process conditions as follows: seed load 1%, evaporation temperature 60℃, stirring rate 200r/min, vacuum degree 0.07MPa, the natural concentration of fermentation broth. Under the optimum process conditions, medium size of the crystals was 916μm and coefficient of variation was 57%. In addition, some quality indexes of sodium gluconate products were determined, the results showed that the quality of the products was better.